Circadian rhythm, nature’s mechanism to regulate our awake and sleep times over the course of 24 hours, gets all the attention. For new parents however, the 30- 90 minute wakeful/sleepy pattern, one of humans' repeating ultradian rhythms, really rules their days (and nights). There are a lot books written about baby sleep and getting baby on a schedule and they're all based on this cycle. Understanding how this pattern works can help cut through all the information to help baby stay calm and happy.
Circadian rhythm and sleep cycles are controlled by serotonin and melatonin. Serotonin produces alertness during the day and is triggered by daylight, and melatonin produces sleepiness during the night and is triggered by darkness. Simple enough, right? If we visualize the cycle, baby is wakeful at the top of the curve (45 minutes after waking up) and then sleepy at the bottom of the cycle (90 minutes after waking).
Here’s the tricky part though; in full-term newborns, melatonin isn’t fully produced until weeks 9-12 so they don’t start out on a 90 minute cycle, they build up to it. Getting baby down to rest before their internal "clock dings" is key to ensuring baby doesn't enter into another wakeful period which makes them fussy.
Here's a breakdown of newborns' basic awake and sleep times:
Weeks 0-2: Baby is awake for a maximum of 30 minutes. Most of this time is spent feeding and baby will appear sleepy even during wakeful periods, often falling back asleep with no help at all.
Weeks 3-8: Baby is awake for a maximum of 45 minutes. You'll notice baby is more wakeful around week 8; s/he won't just go right back to sleep like s/he used to and may need your help to stay asleep. Baby wearing, white noise, giving a pacifier to help sleep are all fine to do because at this age baby needs your help to get and stay sleep.
Weeks 8-12: Baby is working on and eventually awake for 60 minutes. Napping will become longer during these weeks as well but it's perfectly fine and even recommended to help baby with napping when s/he pops up after 10-15 minutes or so by giving a pacifier, using white noise etc. You're not creating bad habits, baby simply needs a little help to not fully awaken because the systems that make seratonin and melatonin are not quite mature yet.
Weeks 12 - 18: Baby is working on and eventually is awake for 90 minutes. Baby is even more alert and still may need help getting and staying asleep. If your goal is to have baby eventuall sleep through the night, try not to pick baby up if she wakes before a 90 minute nap is done, rather stay near to comfort with patting on the back or giving pacifer while baby is still asleep but exhibiting signs of waking up like twitching or moving her head back and forth.
Weeks 18 -24: Baby is awake for 90+ minutes and consolidates naps now. There may be fewer naps that vary in length but a nap of at least 90 minutes will provide adequate rest. S/he will usually be awake for some increment of 90 minutes (11⁄2 hours, 3 hours, 4 1⁄2 hours).
If your goal is to have baby sleep long stretches overnight without feeding, which is really just one big nap consolidation, the 4 month well check is a great time to start talking with your pediatrian about whether baby is developmentally ready to sleep for at least 6 hours uninterrupted.
An important note: Sometimes even though we're doing everything right, babies cry. A LOT. Could be colic, could be overstimulation, could be reflux, could be baby trying out her lungs. Even if you follow this blog or any sleep advice exactly as it’s written, babies are not robots and will still cry. You’re doing a great job, but if you’re concerned about baby’s crying or health, please contact your pediatrician.